This invention relates generally to soil conditioning and particularly pertains to a method for desalination and reclamation of irrigated soil.
Soils irrigated with water of a high total dissolved solids (salt) content (500 ppm or greater) typically accumulate salts and/or alkalis that inhibit crop growth. Salts, mainly chlorides, carbonates, and sulfates or sodium, potassium, calcium, and magnesium are typically measured as the electrical conductivity (mmhos./cm..sup.2) of a saturation extract of the soil. An electrical conductivity greater than 4.0 mmhos./cm..sup.2 indicates that a soil is saline. In saline soils the effect of salts on plants is mainly indirect; that is, the effect of the salts on osmotic water potential, and the resultant reduced uptake of water by germinating seeds and roots of established plants. An alkaline solid (sodic) is a soil that has accumulated large amounts of sodium and is determined by calculating the sodium absorption ratio (SAR) of the saturation extract of the soil. An SAR greater that 15 indicates that a soil is alkaline. In alkaline soils crop growth is inhibited by sodium toxicity. Typically, alkaline soils are also saline compounding toxic sodium levels with reduced plant water uptake ability. Therefore, alkaline-saline soils are particularly deleterious to seed germination and plant growth. It becomes advantageous to remove sodium from the alkaline soils and calcium from calcareous saline soils.
Soil salinity/alkalinity is highly influenced by physical characteristics of the soil such as, the hydraulic conductivity and infiltration rates. Climate, as it affects the evapotranspiration rates from the soil and plants, also plays an important role in the extent of salt and/or alkali accumulation in the soil. Finally, agricultural irrigation practices have an important part in determining whether salts and/or alkalis will accumulate in soils. Known techniques and practices for removing salts and/or alkalis are often expensive and relatively ineffective. One such technique is to add cattle manure and/or green manures into the top soil to maintain a porous condition that will induce infiltration of water into the soil. In high temperature climates, typical of irrigated arid regions, these organic additions decay rapidly and their influence on soil physical properties is lost. Another technique involves the application of gypsum, sulfuric acid, or elemental sulfur to facilitate the removal of sodium. This technique requires large quantities of materials (typically on the order of tons/acre), considerable manpower and fuel, and is only temporarily effective. Yet another technique previously employed is the mechanical practice of chiseling, deep plowing, and slip plowing to improve water movement into and through the soil profile. This practice is of a relatively short-term benefit because the soils tend to slake down and close up after being irrigated requiring reworking on a yearly basis.
It is therefore desirable to have a method for desalination and reclamation of irrigated soil which is relatively inexpensive, easy to perform and effective to remove the salts and/or alkalis in order to enhance crop yield.